The present invention relates to a technical field of a cup seal, and a plunger type master cylinder including the cup seal, used in a cylinder device configured of a cylinder, such as a master cylinder of a brake or clutch in a vehicle such as an automobile, and a sliding member disposed in such a way that it can move inside the cylinder relative to the axial direction thereof.
To date, in a hydraulic brake system or hydraulic clutch system of an automobile, a master cylinder which generates hydraulic pressure in accordance with a tread force of a brake pedal or clutch pedal has been used to operate a brake or clutch. As the master cylinder, a plunger type master cylinder including a cylinder main body which has a cylinder hole, a piston, slidably inserted into the cylinder hole, which demarcates a hydraulic chamber, a communication passage, provided in the cylinder main body, which communicates with a reservoir, a relief port, formed in the piston, which connects the communication passage and hydraulic chamber, and a seal member which, as well as being housed in a depressed portion of the inner peripheral surface of the cylinder hole of the cylinder main body, is slidably passed through by the piston, and seals a space between the inner peripheral surface of the cylinder hole and the outer peripheral surface of the piston, is known from JP-A-2006-123879.
With the plunger type master cylinder, at an inoperative time, the relief port of the piston and the communication passage not being blocked off by the seal member, the hydraulic chamber communicates with the reservoir via the relief port and communication passage. Consequently, at the inoperative time, the inside of the hydraulic chamber is at atmospheric pressure, and no hydraulic pressure is generated. On the piston advancing to the hydraulic chamber side due to a pressing down upon the brake pedal or clutch pedal, the relief port and communication passage are blocked off by the seal member, and the hydraulic chamber is blocked off from the reservoir. Because of this, hydraulic pressure is generated in the hydraulic chamber along with the advancing of the piston.
A sealing function for preventing the hydraulic pressure from leaking when the hydraulic pressure is generated by the advancing of the piston, and a pumping function, which is a liquid supply function supplying braking liquid of the reservoir to the hydraulic chamber in order to increase responsiveness when the piston withdraws, are required of the seal member used in the plunger type master cylinder. Therein, in order to cause the seal member to fulfill these two functions, a cup seal is employed as the seal member.
A master cylinder using a cup seal of which a radial direction cross-section is formed in an E shape as the cup seal is proposed by the previously described 2006-123879. The E-type cup seal described in 2006-123879 includes a circular base portion, an inner peripheral lip portion projecting from the inner peripheral side of the base portion, an outer peripheral lip portion projecting from the outer peripheral side of the base portion, and an intermediate lip portion projecting from the base portion between the inner peripheral lip portion and the outer peripheral lip portion.
The inner peripheral lip portion, outer peripheral lip portion, and intermediate lip portion are all formed in a continuous circular shape. Also, a plurality of cutout grooves are formed, leaving intervals in the peripheral direction, in the leading end side of the intermediate lip portion. Then, by causing the hydraulic fluid to flow through the plurality of cutout grooves when loading hydraulic fluid into the master cylinder when removing the air of the master cylinder, it is possible to supply sufficient hydraulic fluid.
However, with the cup seal described in JP-A-2006-123879, the intermediate lip portion is provided continuously over the whole periphery. For this reason, the intermediate lip portion exerts a rib effect, and the base portion of the cup seal is comparatively stiff. In this case, the plurality of cutout grooves are formed in the leading end portion of the intermediate lip portion but, even though the cutout grooves are formed, the stiffness of the base portion of the cup seal barely changes. When the base portion is stiff in this way, it is difficult for the base portion to elastically deform. Consequently, the base portion barely elastically deforming when supplying hydraulic fluid to the master cylinder, the base portion does not greatly separate from a side wall of a housing depressed portion housing the cup seal of the master cylinder. For this reason, no large gap being formed between the base portion of the cup seal and the housing depressed portion, it is difficult to form a liquid passage with a sufficiently large passage area. Consequently, even when forming the cutout grooves in the leading end portion of the intermediate lip portion, there is a problem in that there is a limit to the supply of the hydraulic fluid, and a certain amount of time is needed to supply a sufficient amount of hydraulic fluid.